The present invention relates to a method of manufacturing a circuit board and its manufacturing apparatus.
With a recent trend of electronic equipment becoming more miniaturized and higher in component density, a circuit board to mount electronic components has evolved from a conventional single board to a double-sided board and a multilayer board. Accordingly, it is necessary to develop a higher density circuit board capable of integrating as many circuits as possible thereon.
For the manufacture of a high density circuit board, the employment of a laser beam machining method capable of high-speed fine machining is now studied in place of a conventional method of making a hole (through-hole) in a board by drilling that has been widely employed. Also, Japanese Laid-Open Patent No. 6-268345 discloses a method of drilling by a laser beam and a circuit forming board wherein layer connection is made by a means using a conductive paste.
In the technology of fine hole forming and layer connection by using a conductive paste, a slight amount of foreign matter can cause defective connection. In this technology, a board material coated with a film material is drilled. The film material is used as a mask to fill a conductive paste into fine holes. Accordingly, it is necessary to keep clean the entire board including the film material.
However, both of the drilling and laser beam machining methods cause generation of a large volume of chips. And there arises a problem such that the chips stick to the board material and clog the connecting hole (through-hole). Also, there is a fear that even a slight amount of dust in the air may cause clogging of the fine hole. The board material is cleaned before a conductive paste is filled into the hole. After using a film material as a mask for filling the conductive paste, the film material bonded to the board material is removed from the board material. Accordingly, the film material is very low in adhesion to the board material, and the film material is liable to come off the board material.
FIG. 8(a) shows a top plan view of a drilling portion in a conventional method of manufacturing a circuit forming board, and FIG. 8(b) shows a cross-sectional view of the drilling portion. As shown in FIGS. 8(b) and 8(b), polyethylene phthalate (PET) sheets 4a, 4b bonded to the portions of especially low in adhesion may sometimes peel off the board material 1. When such peeling takes place around a through-hole, conductive paste 31 for connection may spread into peeled portion 33 and, consequently, shorting 32 may take place between adjacent through-holes.
Accordingly, it is required to clean the board material without giving excessive stresses to the board material 1 and also without peeling the film materials 4a, 4b. However, it is very difficult to satisfy both of these requirements, resulting in insufficient cleaning of the board material.
As described above, the purpose of drilling the board material 1 is to connect the circuits formed on the surface and back or interlayer of the board with each other. After drilling, a connecting means is formed by metal-plating or conductive paste filling.
The sizes of holes and connecting means in a high density circuit board are very small and fine. Accordingly, even very fine foreign matter can cause serious influences to the reliability of connecting means. Therefore, it is necessary to completely remove such foreign matter. However, in a conventional method, film material 4a, 4b serving as a mask peels off when a great stress is given to the board material 1. And then the film material loses its function as a mask or a conductive paste spreads into the board material. Consequently, there arises a problem such as worsening of the reliability in insulation.
The present invention is intended to provide a method of manufacturing a low-cost highly reliable circuit board and its manufacturing apparatus, realizing a board material having high-quality fine holes.
A method of manufacturing a circuit board of the present invention comprises:
(a) a process for preparing a film-coated board material by bonding a film material to the surface of a board material, wherein the film material is bonded to at least either the surface or back of the board material;
(b) a process for forming a hole in the film-coated board material, wherein the hole has at least either a through-hole or a non-through-hole, unnecessary material is produced when the hole is formed and the unnecessary material sticks to the board material, and the unnecessary material has at least one selected from the group consisting of affected portion, affected material and foreign material which are generated from the board material; and
(c) a process for selectively removing the unnecessary material sticking to the film-coated board material without peeling the film material off the board material.
Preferably, the method of manufacturing a circuit board, further comprises:
(d) a process for disposing a conductive material in the hole formed in the film-coated board material, using the film material as a mask; and
(e) a process for removing the film material from the film-coated board material including the conductive material.
Further preferably, the hole forming process includes a step of forming a hole by applying a laser beam, and the application of the laser beam causes generation of the unnecessary material.
Preferably, the process for selectively removing the unnecessary material sticking to the film-coated board material from the film-coated board material includes a process for selectively removing the unnecessary material from the film-coated board material by vibrational energy generated from a supersonic oscillator while submerging the film-coated board material into a cleaning tank provided with a cleaning solution and the supersonic oscillator.
Further preferably, the process for selectively removing the unnecessary material sticking to the film-coated board material from the film-coated board material includes a process wherein a flow of the cleaning solution is generated between the supersonic oscillator and the film-coated board material, and the film-coated board material is subjected to supersonic cleaning while the liquid flow is applied to the board material.
Further preferably, the process for selectively removing the unnecessary material sticking to the film-coated board material from the film-coated board material includes a process wherein the film-coated board material is subjected to supersonic cleaning while a plate material is disposed between the supersonic oscillator and the film-coated board material, and the volume of supersonic energy reaching the film-coated board material is controlled by the plate material.
Further preferably, the process for selectively removing the unnecessary material sticking to the film-coated board material from the film-coated board material includes a process wherein the film-coated board material is subjected to supersonic cleaning while the film-coated board material is held between plate materials.
Further preferably, the process for selectively removing the unnecessary material sticking to the film-coated board material from the film-coated board material without peeling the film material off the board material includes
(i) a cleaning process for selectively removing the unnecessary material from the film-coated board material while submerging the film-coated board material into a cleaning tank containing a cleaning solution,
(ii) a process for taking the film-coated board material out of the cleaning tank after removing the unnecessary material, and
(iii) a process for removing at least one of the remaining unnecessary material and cleaning solution sticking to the film-coated board material taken out of the cleaning tank, wherein the film-coated board material is heated in at least one of the process (i) and process (iii).
A cleaning device of the present invention serves to remove the unnecessary material from a film-coated board material to which unnecessary material is sticking. The film-coated board material comprises a board material and a film material as a mask bonded to the board material; the film material is bonded to the board material in a manner such that it can be peeled off the film-coated board material; the unnecessary material is produced when a hole is formed in the film-coated board material; and the unnecessary material is sticking to the film-coated board material.
The cleaning device comprises
a cleaning tank;
a cleaning solution provided in the cleaning tank;
a supersonic oscillator installed in the cleaning solution;
a feeding device which feeds the film-coated board material into the cleaning solution while retaining the film-coated board material; and
a selective removing means which selectively removes the unnecessary material from the film-coated board material without peeling the film material.
The selective removing means includes at least one selected from the group consisting of:
(i) a water flow generator which generates a water flow between the supersonic oscillator and the film-coated board material located above the supersonic oscillator;
(ii) a diffusing plate installed between the supersonic oscillator and the film-coated board material located above the supersonic oscillator; and
(iii) resonance control plates which hold the film-coated board material therebetween.
Due to this configuration, it is possible to obtain a board material having clean and high-quality fine holes and also a low-cost highly reliable circuit board.